EXA/6xx/7xx: accelerate PictOpOver with component alpha

Subpixel text rendering is typically done with a solid src and
a pixmap mask. Traditionally, this cannot be accelerated in a single
pass and requires two passes [1]. However, we can cheat a little
with a constant blend color.

We can use:
const.A = src.A / src.A
const.R = src.R / src.A
const.G = src.G / src.A
const.B = src.B / src.A

dst.A = const.A * (src.A * mask.A) + (1 - (src.A * mask.A)) * dst.A
dst.R = const.R * (src.A * mask.R) + (1 - (src.A * mask.R)) * dst.R
dst.G = const.G * (src.A * mask.G) + (1 - (src.A * mask.G)) * dst.G
dst.B = const.B * (src.A * mask.B) + (1 - (src.A * mask.B)) * dst.B

This only needs a single source value. src.A is cancelled down in
the right places.

[1] http://anholt.livejournal.com/32058.html

r6xx still be used on some machine,
Ported from commit 4375a6e75e5d41139be7031a0dee58c057ecbd07.

Signed-off-by: Tan Hu <tan.hu@zte.com.cn>
Reviewed-by: Grigori Goronzy <greg@chown.ath.cx>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/r600_state.h b/src/r600_state.h
index fa777e8b..fda297d3 100644
--- a/src/r600_state.h
+++ b/src/r600_state.h
@@ -266,6 +266,8 @@ r600_wait_3d_idle(ScrnInfoPtr pScrn);
 void
 r600_start_3d(ScrnInfoPtr pScrn);
 void
+r600_set_blend_color(ScrnInfoPtr pScrn, float *color);
+void
 r600_set_render_target(ScrnInfoPtr pScrn, cb_config_t *cb_conf, uint32_t domain);
 void
 r600_cp_wait_vline_sync(ScrnInfoPtr pScrn, PixmapPtr pPix, xf86CrtcPtr crtc, int start, int stop);